The polyphenylene ethers are a widely used class of thermoplastic engineering resins characterized by excellent hydrolytic stability, dimensional stability, toughness, heat resistance and dielectric properties. However, polyphenylene ethers are deficient in that their tensile properties and impact strength are poor. Therefore, there is a continuing search for means for modifying polyphenylene ethers to improve these other properties.
It would be desirable to improve the impact resistance and tensile properties of polyphenylene ethers by blending them with another polymer such as a thermoplastic elastomer (TPE). Potential advantages of blending polyphenylene ethers with a TPE include providing a polyphenylene ether blend with a lower modulus, higher tensile elongation, and higher impact strength than unblended polyphenylene ethers, and a TPE product with improved heat distortion temperature compared to the unblended TPE. However, in general, physical blending of polymers does not provide a complete solution to the problems of the poor impact and tensile properties of polyphenylene ethers because the TPE polymers which would improve the impact resistance of the polyphenylene ethers are generally immiscible with the polyphenylene ethers and frequently undergo phase segregation in molded parts resulting in delamination and/or brittleness. Such parts typically contain large, incompletely dispersed polyphenylene ether particles and no phase interaction between the two resin phases. As a result, interphases between blend component domains are areas of weakness resulting in mechanical failure.
It has been previously proposed to blend polyphenylene ethers with elastomeric polyesters. For example, U.S. Pat. No. 4,831,087 (Brown) describes resin blends prepared from a polyphenylene ether having a low proportion of unneutralized amino nitrogen; an elastomeric polyester or blend thereof with a poly(ethylene terephthalate) or poly(butylene terephthalate); and at least one polymer containing a substantial proportion of aromatic polycarbonate units as a compatibilizing agent. The blends are free from extraneous impact modifiers.
However, these blends require the presence of a compatibilizing agent. Further, prior to blending it is often necessary to remove the thermally labile aminoalkyl-substituted end groups and other amine constituents frequently present as impurities in the polyphenylene ether component. Such expedients as the use of amine quenchers and/or vacuum venting of the polyphenylene ether are effective in decreasing amino nitrogen content, but add a step to the processing operation which may be undesirable under certain circumstances.
There continues to be a need for polyphenylene ether--TPE blends that do not require the presence of a compatibilizer and/or low nitrogen polyphenylene ethers.